Sleeping sickness (human African trypanosomiasis, HAT) is caused by parasites of the T. brucei complex and is transmitted via tsetse flies.

• T. b. rhodesiense causes the East African form and T. b. gambiense the West African form; these two forms are epidemiologically and clinically distinct illnesses.
• Humans are the only reservoir for T. b. gambiense; infection occurs primarily in rural populations and rarely develops in tourists. T. b. rhodesiense has reservoirs in antelope and cattle; tourists can be infected when visiting areas where infected game and vectors are present.
• HAT was nearly eradicated in the mid-1960s, resurged in the 1990s, and is now decreasing in incidence because of renewed control activities. Fewer than 10,000 cases were reported to the World Health Organization in 2009.